1. Field of the Invention
The present invention relates to a plasma processing apparatus for manufacturing semiconductors and, more particularly, to an inductively coupled plasma (ICP) processing apparatus utilizing radio frequencies.
2. Description of the Related Art
Capacitively coupled plasma processing apparatuses utilizing radio frequencies have been widely used as apparatuses for performing a plasma process on semiconductor substrates in a reaction chamber. This process is to generate an electrical field between parallel plate type electrodes by applying radio frequency power to either or both of them to cause plasma discharge, and it has been applied to plasma CVD processes and RIE processes.
However, conventional parallel plate type plasma processing apparatuses have exhibited limited capability in generating high density plasma. Further, demands for ultra-fine processing of semiconductor devices in these days has increased so as to provide uniform plasma with higher density and controlling it with high accuracy.
Thus, ECR (electron-cyclotron resonance) plasma and ICP (inductively coupled plasma) and the like have been conceived as an example exceeding improvements over the conventional parallel plate type capacitively coupled plasma.
Generally, the ECR method is to apply a strong magnetic field to plasma using a magnetic field generating coil and to apply a microwave (at 2.45 GHz in general) in parallel with the magnetic field, thereby increasing the plasma density. Electrons at a cyclotron frequency are accelerated by absorbing wave energy of the microwave that penetrates through the plasma, which increases the frequency of collision between neutral particles and electrons to increase the plasma density. According to this method, however, it is difficult to obtain uniform plasma having a large diameter because it involves a large and complicated apparatus. As an improvement over this method, there is a method wherein power at a radio frequency in a VHF band (from 100 MHz to 1 GHz) is applied to an antenna which is electrically floating (not grounded) to generate an electrical field in parallel with the traveling direction of electrons to accelerate electrons, thereby producing high density plasma. However, this method also has a problem in that the length of such an antenna must be increased when a high frequency such as a radio frequency in a frequency band lower than VHF is used, which results in an increase in apparatus dimensions.
The ICP method is to apply power at a radio frequency (in the range from 100 kHz to 100 MHz) to an antenna in the form of a coil or loop wound around the periphery of a container made of an insulator to induce a high frequency electrical field, thereby accelerating electrons to produce plasma. However, this method has a problem in that a very expensive bell jar made of alumina or quartz having a large diameter is required to process an object having a large diameter, which results in an increase in the cost of the apparatus. As an improvement on this, there is a method wherein an antenna in the form of a loop is provided in a reaction chamber. However, this method also has a problem in that the coil or loop used is difficult to process to provide it with insulating properties because it has a circular configuration. As a result of an insufficient insulating process, arcing or abnormal discharge occurs between the coil or loop and plasma generated to make the plasma unstable and, in addition, the density of the plasma thus generated is limited because high RF power can not be used.
It is therefore an object of the present invention to provide an inductively coupled plasma processing apparatus which generates uniform and stable plasma with high density.
It is another object of the present invention to provide an inductively coupled plasma processing apparatus capable of controlling a spatial profile of plasma with high accuracy.
It is still another object of the present invention to provide an inductively coupled plasma processing apparatus which does not need additional devices and which has a compact body.
In order to achieve the above-described object, a plasma processing apparatus according to the present invention comprises means as described below.
A plasma processing apparatus for processing an object to be processed utilizing plasma according to the present invention comprises:
an evacuated reaction chamber for processing the object to be processed therein;
an antenna provided in the inside of the reaction chamber formed by a plurality of linear conductors; and
an RF power supply connected to one end of the plurality of linear conductors.
Specifically, the antenna is constituted by at least three linear conductors disposed such that they radially extend from the center of the antenna at equal intervals from each other, and each of the linear conductors is grounded at one end thereof and is connected to the RF power supply at the other end thereof.
Alternatively, the antenna may be formed by at least three linear conductors having the same length disposed at the same distance from the center of the antenna.
While the plurality of linear conductors are preferably connected to each other in parallel, they may be connected to each other in series.
Further, the antenna may have a structure formed by two layers which are in parallel with each other.
Preferably, the surface of the plurality of linear conductors of the antenna is insulated.
More preferably, the antenna may have a hollow tubular structure to allow cooling water to flow therethrough.
A plasma processing apparatus for semiconductors according to the present invention further comprises magnetic field generating means for generating a magnetic field in a direction orthogonal to an induced electrical field.